High-capacity positive electrode active material

ABSTRACT

This disclosure provides a positive electrode active lithium-excess metal oxide with composition Li x M y O 2  (0.6≦y≦0.85 and 0≦x+y≦2) for a lithium secondary battery with a high reversible capacity that is insensitive with respect to cation-disorder. The material exhibits a high capacity without the requirement of overcharge during the first cycles.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application claims priority to U.S. provisional patentapplication No. 61/708,963, filed Oct. 2, 2012, the entire contents ofwhich are hereby incorporated by reference herein.

TECHNICAL FIELD

The present disclosure relates to a discharge-positive electrode (alsoreferred to as cathode) for a lithium secondary battery that exhibits alarge reversible capacity and does not require overcharge (the chargingbeyond the theoretical capacity limit) during the first cycles, and asynthesis route for producing the same.

BACKGROUND

Li Battery Cathode Materials:

The positive electrode (cathode) material is the limiting factor in theproduction of high capacity and high energy density lithium ionbatteries. An important class of cathode materials for secondary lithiumbatteries is constituted by rock-salt type layered lithium metal oxidesof the general composition LiMO₂, where M is a metallic species or amixture of several such. In such layered oxides, every second plane in<111> direction (from F-3m cubic system) contains alternating lithiumcations or cations of species M (M. S. Whittingham, Science 192 (1976)1126-1127; M. S. Whittingham, Chemical Reviews 104 (2004) 4271-4302). Ithas been typical in the field of batteries to look for well-orderedlayered cathodes, in which the Li and M cations are well separated indistinct (111) layers. For example, capacity degrading in LiNiO₂ can beattributed to the migration of nickel cations to the lithium layer (C.Delmas et al., Journal of Power Sources 68 (1997) 120-125). IntroducingMn to the compound improves its layeredness and results in significantlybetter capacity retention (K. Kang et al., Science 311 (2006) 977-980).Similarly, cation mixing is believed to have a strong negative impact onthe electrochemical performance of Li(Li,Ni,Mn,Co)O₂ (X. Zhang et al.,J. Power Sources 195 (2010) 1292-1301). The capacity of mostwell-ordered layered cathode materials has been limited to 150-180 mAh/gwhich corresponds to ≈0.5 to 0.65 Li ions per LiMO₂ formula unit (T.Ohzuku, Y. Makimura, Chemistry Letters 30 (2001) 744-745; J. Choi, A.Manthiram, J. Electrochem. Soc. 152 (2005) A1714-A1718). To achievehigher capacity, complex overcharging schemes have been developed, butthese are difficult to implement in the manufacturing of batteries. Forexample, some Li(Li,Ni,Co,Mn)O₂ compounds are overcharged in the firstcycle at a voltage above 4.7 V in order to release oxygen, and achieve ahigher capacity in the subsequent cycles (M. M. Thackeray et al., J.Mater. Chem. 17 (2007) 3112-3125; A. R. Armstrong et al., J. Am. Chem.Soc. 128 (2006) 8694-8698). But this overcharge process is moreexpensive to implement and leads to cathode materials with limitedlong-term stability as well as reduced charge/discharge rate capability.Thus, overcharging may lead to oxygen evolution and poses a potentialsafety risk, and adds cost and complications to battery manufacturing.

SUMMARY

Described herein, among other things, is a discharge-positive electrodematerial for a lithium secondary battery that exhibits a largereversible capacity of more than 150 mAh/g. In some embodiments, thematerial is a (rock-salt type) lithium metal oxide with compositionLi_(x)M_(y)O₂ with 0.6≦y≦0.85 and 0≦x+y≦2, where M is a mixture ofmetallic elements including at least one of Al, Ti, V, Cr, Mn, Fe, Co,Ni, Cu, Zn, Zr, Nb, Mo, Ru, Sn, Sb. The material is capable of cationmixing. In contrast to existing lithium excess metal oxide activematerials, the material presented here does not require overchargeduring the first cycles.

In some embodiments, a provided material is a lithium metal oxidecharacterized by a general formula Li_(x)M_(y)O₂ wherein 0.6≦y≦0.85,0≦x+y≦2, and M being one or more of a metallic species chosen from thegroup consisting of Al, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Nb, Mo,Ru, Sn and Sb; said oxide, when characterized by XRD, showing

-   -   a. a peak whose intensity I′ is the largest in the range 16-22        degrees 2θ, such as the (003) peak in structures with space        group R-3m, and the (001) peak in structures with space group        P-3m1, and    -   b. a peak whose intensity I″ is the largest in the range 42-46        degrees 2θ, such as the (104) peak in structures with space        group R-3m, and the (011) peak in structures with space group        P-3m1;    -   the oxide characterized in that subjecting said oxide to at        least one lithium ion extraction-insertion cycle results in a        reduction of the ratio of I′/I″.        In some embodiments, the intensity I′ is reduced by at least 10%        (e.g., at least 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, or 50%)        upon subjecting the oxide to at least one lithium ion        extraction-insertion cycle. In some embodiments, the intensity        I′ is reduced by at least 10% (e.g., at least 10%, 15%, 20%,        25%, 30%, 35%, 40%, 45%, or 50%) upon subjecting the oxide to        ten lithium ion extraction-insertion cycles. In some        embodiments, the ratio I′/I″ is reduced by at least 10% (e.g.,        at least 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, or 50%) upon        subjecting the oxide to at least one lithium ion        extraction-insertion cycle. In some embodiments, the ratio I′/I″        is reduced by at least 10% (e.g., at least 10%, 15%, 20%, 25%,        30%, 35%, 40%, 45%, or 50%) upon subjecting the oxide to ten        lithium ion extraction-insertion cycles.

In some embodiments, the distribution of cations becomes more randomand/or more disordered among cation layers upon subjecting an oxide toat least one lithium ion extraction-insertion cycle. In someembodiments, the distribution of cations becomes more uniformlydistributed over the cation layers (as opposed to strict segregationinto Li and M layers) upon subjecting an oxide to at least one lithiumion extraction-insertion cycle.

In some embodiments, a provided material is a lithium metal oxidecharacterized by a general formula Li_(x)M_(y)O₂ wherein 0.6≦y≦0.85,0≦x+y≦2, and M being one or more of a metallic species chosen from thegroup consisting of Al, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Nb, Mo,Ru, Sn and Sb; said oxide, as synthesized, showing a random or partiallyrandom distribution of Li cations and M cations in the oxygenarrangement of the rock-salt structure, as measurable by XRD. In someembodiments, such oxides, when characterized by XRD, show a peak whoseintensity I′ is the largest in the range 16-22 degrees 2θ, and a peakwhose intensity I″ is the largest in the range 42-46 degrees 2θ. In someembodiments, is essentially zero, so that I′/I″≦0.01.

In certain embodiments of provided oxides, the absence of oxygenoxidation is characterized by a first charge capacity of at least 150mAh/g when charging at room temperature at C/20 rate which is the rateto potentially utilize the full theoretical capacity C_(max) in 20hours.

In certain embodiments of provided oxides, the distance between any twoneighboring oxygen planes in any lattice direction is less than 2.55 Åupon subjecting the oxide to at least one lithium insertion-extractioncycle.

In certain embodiments, an oxide is Li_(1+x)Mo_(2x)Cr_(1−3x)O₂, wherein0.15<x<0.333. In certain embodiments, an oxide isLi_(1+x)Ni_((2−4x)/3)M_((1+x)/4)O₂, wherein 0.15<x≦0.3 and M is Sb orNb. In certain embodiments, an oxide isLi_(1+x)Ni_((3−5x)/4)Mo_((1+x)/4)O₂, wherein 0.15<x≦0.3. In someembodiments, an oxide is Li_(1+x)Ru_(2x)M_(1−3x)O₂, wherein 0.15<x<0.333and M is Co, Ni, or Fe. In certain embodiments, an oxide isLi_(1+x)Fe_(1-y)Nb_(y)O₂, wherein 0.15<x≦0.3 and 0<y≦0.3. In someembodiments, an oxide is Li(Li_(0.233)Mo_(0.467)Cr_(0.3))O₂.

In some embodiments, an oxide has a substoichiometric amount of lithium.In certain embodiments, an oxide has the formulaLi_(((4−x)/3)-w)(Mo_(2−2x)/3)Cr_(x))O₂, wherein:0<x≦0.5; and0≦w≦0.2;wherein w represents a lithium deficiency. In some embodiments, an oxidehas the formula Li_((1.233-w))Mo_(0.467)Cr_(0.3)O₂.

In some embodiments, the present disclosure provides an electrodecomprising at least one oxide disclosed herein. In some embodiments, thepresent disclosure provides a coated electrode material comprising atleast one oxide disclosed herein. In certain embodiments, a coatedelectrode material has a coating comprising a member selected from thegroup consisting of carbon, MgO, Al₂O₃, SiO₂, TiO₂, ZnO, SnO₂, ZrO₂,Li₂O-2B₂O₃ glass, phosphates, and combinations thereof. In someembodiments, a coating comprises a phosphate is selected from the groupconsisting of AlPO₄, Li₄P₂O₇, and Li₃PO₄. In some embodiments, a coatingcomprises carbon.

In some embodiments, a provided electrode composition comprises carbonblack, a binder, and a coated electrode material described herein.

In certain embodiments, the present disclosure provides methods ofpreparing Li_(1+x)Mo_(2x)Cr_(1−3x)O₂, wherein 0.15<x<0.333, the methodcomprising contacting precursors Li₂CO₃, MoO₂, and Cr₃(OH)₂(OOCCH₃)₇ atan elevated temperature. In some embodiments,Li(Li_((1−x)/3)Mo_((2−2x)/3)Cr_(x))O₂ isLi(Li_(0.233)Mo_(0.467)Cr_(0.3))O₂. In certain embodiments, the elevatedtemperature is from about 800° C. to 1200° C. In certain embodiments,the elevated temperature is from about 800° C. to 1000° C. In someembodiments, the methods comprise milling the precursors. In someembodiments, the methods comprise dispersing the precursors in asuitable solvent prior to milling, and drying the resulting mixture.

Without wishing to be bound by any particular theory, it is believedthat in some embodiments an amount of lithium may be lost duringsynthesis of certain oxides. For example, in some embodiments of anoxide such as Li_(1.233)Mo_(0.467)Cr_(0.3)O₂, wherein the formularepresents theoretical stoichiometry, the experimental stoichiometry canbe about Li_(1.211)Mo_(0.467)Cr_(0.3)O₂. In some embodiments, theprovided methods utilize Li₂CO₃ in excess of the stoichiometric amountneeded to produce the desired final compound.

In certain embodiments, the present disclosure provides methods ofcoating Li_(1+x)Mo_(2x)Cr_(1−3x)O₂, wherein 0.15<x<0.333, the methodcomprising contacting a suitable coating material withLi_(1+x)Mo_(2x)Cr_(1−3x)O₂ at an elevated temperature. In someembodiments, the method comprises milling the suitable coating materialwith Li(Li_((1−x)/3)Mo_((2−2x)/3)Cr_(x))O₂. In certain embodiments, theweight ratio of Li(Li_((1−x)/3)Mo_((2−2x)/3)Cr_(x))O₂ to the suitablecoating material is from about 90:10 to about 70:30 (e.g., about 90:10,85:15, 80:20, 75:25, or 70:30). In some embodiments, the elevatedtemperature is from about 400° C. to about 800° C. In certainembodiments, the suitable coating material is carbon. In someembodiments, the suitable coating material is a carbon precursor. Insome embodiments, the carbon precursor converts to carbon at an elevatedtemperature. In some embodiments, the carbon precursor is acarbohydrate. In some embodiments, the carbon precursor is sucrose.

The present disclosure also provides lithium batteries and lithium-ioncells comprising an electrode material described herein. The presentdisclosure further provides devices comprising such lithium batteriesand lithium-ion cells. In some embodiments, a device is a portableelectronic device, an automobile, or an energy storage system.

Other features, objects, and advantages of the present disclosure areapparent in the detailed description that follows. It should beunderstood, however, that the detailed description, while indicatingembodiments of the present disclosure, is given by way of illustrationonly, not limitation. Various changes and modifications within the scopeof the disclosure will become apparent to those skilled in the art fromthe detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1: Schematic depiction of cation mixing. The distance d_(M-M)between layers containing cation species M is approximately halved upondisordering. In XRD spectra, this effect results in a Bragg reflectionat approximately two times 2θ of the layered material, and an intensitydecrease of the (003) peak in O3-type oxides. The dashed lines in thefigure indicate crystal planes whose stoichiometry are independent ofthe cation ordering. XRD signals corresponding to these planes, such asthe (104) peak in O3-type oxides, can be used as a reference to quantifythe layeredness of a sample.

FIG. 2: X-ray diffraction pattern simulation for cation mixing inLiCoO₂: (A) mixing—no transition metal migration to lithium layer atall. (B) 33.33% mixing—25% of transition metal are in lithium layerwhile 75% are in transition metal layer. (C) 100% mixing—50% oftransition metal are in lithium layers and rest (50%) are in transitionmetal layers. As the mixing level increases, the intensity of (003) peakdecreases while that of (104) peak stays similar. At 100% mixing, thereis no longer a (003) peak.

FIG. 3: Theoretical (maximum) capacity of a number of lithium metaloxides as function of the excess lithium contents. The value of thetheoretical capacity C_(max) was calculated as described in the text.

FIG. 4: Tetrahedral site in rock salt based lithium metal oxidessurrounded only by lithium ions (lighter color balls). Such locallithium-rich geometries occur in compositions with excess lithiumcontents. Darker color balls are oxygen atoms.

FIG. 5: Number of accessible lithium atoms per formula unit ascalculated by a numerical percolation simulation (solid black line).Only lithium atoms that are part of a percolating network of stabilizedtetrahedral sites contribute. The dashed line corresponds to the totalnumber of lithium atoms in the formula unit.

FIG. 6: Minimal expected specific capacity of the same set of compoundsas in FIG. 3. The graph can be understood as a combination of thetheoretical capacity depicted in FIG. 3 and the expected number ofaccessible lithium atoms of FIG. 5.

FIG. 7: XRD patterns of C-coated Li_(1.211)Mo_(0.467)Cr_(0.3)O₂electrodes before and after 10 cycles, 1.5V-4.3V, C/10 (1C=327.486mAg⁻¹)

FIG. 8: The STEM along the [010] zone axis in a C-coatedLi_(1.211)Mo_(0.467)Cr_(0.3)O₂ particle before and after 10 cycles,1.5V-4.3V, C/20 (1C=327.486 mAg⁻¹).

FIG. 9: The voltage profile of C-coated Li_(1.211)Mo_(0.467)Cr_(0.3)O₂when cycled between 1.5V-4.3V at C/20-rate (1C=327.486 mAg⁻¹).

FIG. 10: Region of expected capacity for Li(Li_(x)Mo_(a)Cr_(b))O₂. Thespecific capacity of an actual material is expected to fall into theregion defined by the maximum theoretical capacity (FIG. 3) and theminimal expected capacity (FIG. 5).

DETAILED DESCRIPTION OF CERTAIN EMBODIMENTS

In the present disclosure, high capacity cathode materials were preparedthat do not require an overcharge in the first cycles. In addition,contrary to common belief in the battery field, it is shown thatwell-ordered cathode materials are not needed, and that actually, highlydisordered Li-excess materials can deliver very high reversible Listorage capacity.

Cation Order:

The layeredness of a sample of a LiMO₂ compound can be experimentallyquantified using powder X-ray diffraction (XRD). In well-layeredmaterials, the distance d_(M-M) between layers containing cation speciesM is approximately twice as large as in disordered materials (FIG. 1),and manifests itself in a Cu k-α Bragg reflection at 2θ˜16-22°, such asa (003) peak in R-3m layered oxides, or a (001) peak in P-3m1 layeredoxides. As used herein, “peak A” refers to a peak whose intensity I′ isthe largest in the range 16-22°. The intensity of peak A comes from theplane that mainly composed of metal ions that are strong x-rayscatterers. Therefore, any damage to the layered arrangement of metalion results in the decrease of peak A's intensity, as the metal planenow becomes partially composed of weak x-ray scatterers, such as lithiumions or vacancies. There are, however, also crystal planes whosecompositions are independent of the cation mixing (dashed lines in FIG.1), such as (104) planes in R-3m layered oxides, or (011) planes inP-3m1 layered oxides, which are typically observed at 2θ˜42-46°. Theseplanes give rise to XRD peaks that are insensitive with respect to thecation ordering. As used herein, “peak B” refers to a peak whoseintensity I″ is the largest in the range 42-46°. Therefore, the ratio ofthe intensities of an ordering-sensitive XRD peak at 2θ˜16-22° (peak A)and an ordering-insensitive peak at 2θ˜42-46° (peak B) thus quantifiesthe layeredness of the sample. As an example, FIG. 2 shows how theintensity ratio between (003) peak (peak A) and (104) peak (peak B) ofR-3m LiCoO₂ changes with cation mixing (disordering). When LiCoO₂ isperfectly layered (0% mixing), the ratio is high, and the high intensitycoming from the (003) peak is clearly seen. However, as the cationmixing level (transition metal ions in lithium layers/transition metalions in transition metal layers*100%) increases to 33.33%, now theintensity of the (003) peak is much weaker, while that of (104) peak isstill similar. Finally, as the mixing level increases to 100% (fullycation-disordered), there is no longer (003) peak, and the XRD patternresembles that of Fm-3m cubic disordered rocksalt materials. Asdescribed above, the intensity ratio between the peak A and peak B canbe used to determine the cation mixing level (i.e.cation-disorderedness).

Capacity:

Upon charging lithium is reversibly extracted from the oxide and metalcations are oxidizedLiMO₂

nLi^(⊕) +ne ^(⊖)+Li_(1-n)MO₂

Assuming the extraction of all lithium the maximum theoretical capacityC_(max) is proportional to the number of redox-available electrons n(e)per total mass of the lithiated compound m

$C_{\max} = {\frac{n(e)}{m}{{F\left( {F\mspace{14mu}{is}\mspace{14mu}{Faraday}^{\prime}s\mspace{14mu}{constant}} \right)}.}}$Note that the number of redox-active electrons is not only determined bythe lithium fraction, but also depends on the accessible redox couplesof species M. The theoretical capacity for a number of selectedcompounds of compositions Li_(x)A_(a)B_(b)O₂ is depicted in FIG. 3.

Often a high discrepancy between the theoretical capacity limit and thespecific capacity of a synthesized material is observed because C_(max)only provides a measure for the upper bound of the specific capacity. Incontrast, the most conservative capacity estimate C_(min) is determinedby the number of definitely accessible lithium ions n(Li) per mass ofthe lithiated compound

$C_{\min} = {\frac{n({Li})}{m}{F.}}$

Since ordered layered materials have practical capacities that are muchlower than their theoretical capacities, it is clear that not all the Liions in the material are practically accessible. For Li ions to beaccessible, they have to be able to diffuse in and out of the crystalstructure as that is respectively the discharge and charge process. Thefactors that determine the diffusion of lithium ions in layeredrock-salt type lithium metal oxides are well understood [1]: theactivated states for the lithium ion diffusion through the intercalationmaterial are sites of tetrahedral geometry. The necessary energy forlithium activation, i.e., the lithium diffusion barrier, depends on (i)the oxidation state of the face sharing species of these tetrahedralsites (the higher the oxidation state, the greater the electrostaticrepulsion), and (ii) the size of the tetrahedral sites, which in layeredoxides is in turn mainly determined by the oxygen-layer distanceenclosing a lithium layer in (111) direction (slab distance). The secondparameter, the slab distance, is challenging to predict prior to theactual synthesis of a compound, as cation mixing upon charge-dischargecycling (i.e., the migration of metal cations to the lithium layer andvice versa) can dramatically reduce the slab distance and render a largefraction of lithium inaccessible. However, the first parameter, theoxidation state of face sharing cations, can be systematicallycontrolled by introducing excess lithium to the compound, therebyeffectively altering the stoichiometry to the general compositionformula Li_(1+x)M_(y)O₂ (with lithium excess x). Excess lithium willlead to locally lithium-rich environments, in which lithium is the onlyface sharing species of tetrahedral sites (FIG. 4), resulting in lowlithium diffusion barriers. If the lithium excess is sufficiently large,a percolating network of such easy pathways for Li hopping will beformed, and all lithium ions in this network will be accessible forextraction. FIG. 5 shows the number of accessible lithium ions performula unit as a function of lithium excess as calculated in anumerical percolation simulation.

Combining the information about the available lithium contents, theaccessible redox couples of species M, and the estimated number ofaccessible lithium atoms per formula unit allows calculating the minimalexpected capacity C_(min). The result for the same set of compounds asused in FIG. 3 is shown in FIG. 6. The real capacity of any activematerial is expected to lie within the region defined by C_(min)(x) andC_(max)(x) for any amount of lithium excess x. This estimator is a verypowerful tool for the targeted synthesis of positive electrode activematerials.

Note that the expected minimal capacity C_(min) is insensitive withrespect to cation mixing. Numerical calculations of the accessiblelithium contents for varying degrees of cation mixing have shown thatdisorder even slightly increases the amount of accessible lithium.

EXAMPLES Example 1

Li_(1+x)Mo_(2x)Cr_(1−3x)O₂, [0.15<x<0.333]

To prepare Li_(1+x)Mo_(2x)Cr_(1−3x)O₂, Li₂CO₃, MoO₂, andCr₃(OH)₂(OOCCH₃)₇ were used as precursors. More than 5% excess Li₂CO₃from the stoichiometric amount needed to synthesizeLi_(1+x)Mo_(2x)Cr_(1−3x)O₂, [0<x<0.333] was used to compensate forpossible Li loss during high temperature solid state reaction. Theprecursors were dispersed into acetone and ball-milled for 24 hours anddried overnight to prepare the precursor mixture. The mixture was firedat 1050° C. for 15 hours under Ar gas, and manually ground to obtain thefinal products.

Carbon coating can be applied 1) to prevent Mo and Cr dissolution, 2) toimprove the cycling performance of Li_(1+x)Mo_(2x)Cr_(1−3x)O₂ bydecreasing the particle size upon the carbon coating process, and 3) toimprove electronic conductivity of the compounds. Sucrose (C₁₂H₂₂O₁₁)was used as a carbon precursor, and was mixed in a planetary ball-millwith Li_(1+x)Mo_(2x)Cr_(1−3x)O₂ in weight ratio between 90:10 and 70:30of active material to sucrose. Then the mixture was annealed between400° C. to 800° C. for 2 to 6 hours under Ar gas.

For electrochemical tests, Swagelok cells were assembled under Aratmosphere in a glove box. For the cathode fabrication, ˜70 wt % of theactive compounds, ˜20 wt % of carbon black, and ˜10 wt % of PTFE binderwere intimately mixed by hands or planetary ball-mill.

The above compounds transform from a layered to a disorder rocksalt typelithium metal oxide by cation mixing during cycling. The XRD patterns inFIG. 7 show the structural evolution of the carbon-coatedLi_(1.233)Mo_(0.467)Cr_(0.3)O₂ [x=0.233 in Li_(1+x)Mo_(2x)Cr_(1−3x)O₂]when cycled between 1.5 V-4.3 Vat C/10 (1C=327.486 mAg⁻¹). Arepresentative pattern of layered Li-TM-oxides is seen before cycling,and that of disordered Li-TM-oxides is seen after 10 cycles. Thesignificant decrease in the intensity ratio of (003) peak to (104) peak,the measure of layeredness, indicates that cation mixing triggers thetransformation from a layered to disordered rocksalt type lithium metaloxide.

In FIG. 8 the STEM image of the carbon-coatedLi_(1.233)Mo_(0.467)Cr_(0.3)O₂ particle before cycling shows bright anddark columns corresponding to the atomic columns of(Li⁴⁺/Mo⁴⁺/Cr³⁺)-ions and Li⁺-ions, respectively. Z-contrast decreasesdramatically after 10 cycles. This again indicates increased cationmixing. From Z-contrast information, we calculate 44% of Mo-ions to bein Li layers after 10 cycles at C/20. Together, XRD and STEM confirmthat Li_(1.233)Mo_(0.467)Cr_(0.3)O₂ transforms from a layered todisordered Li-TM-oxide by cation mixing during cycling.

FIG. 9 shows the voltage profile of carbon-coatedLi_(1.233)Mo_(0.467)Cr_(0.3)O₂ when cycled between 1.5 V-4.3 V at C/20.The profile changes after the 1^(st) charge, and shows a high reversiblecapacity at an average voltage of ˜2.8 V [1^(st) discharge=284 mAhg⁻¹(1.07Li), 2^(nd) discharge=265 mAhg⁻¹(1Li), and 10^(th) discharge=262mAhg⁻¹ (0.99Li)]. A voltage profile change indicates the structuralevolution of an electrode material. Thus, the significant change in theprofile after the 1^(st) charge is consistent with our XRD and STEMobservations of heavy cation mixing in the 1^(st) cycle. The highcapacity of carbon-coated Li_(1.233)Mo_(0.467)Cr_(0.3)O₂ isnon-intuitive. It has been seen that cation-mixed layered and disorderedLi-TM-oxides cycle poorly due to their small slab distance which limitsLi diffusion.

FIG. 10 explains why such a high capacity could be achieved indisordered (cation-mixed) Li_(1.233)Mo_(0.467)Cr_(0.3)O₂. At x=0.233,the tetrahedral sites, face-sharing only lithium-ions, form apercolating network in a rock salt structure. The accessible lithiumatoms by percolating network reach ˜0.95Li when x=0.233, correspondingto 250 mAh/g for Li_(1.233)Mo_(0.467)Cr_(0.3)O₂ (FIG. 10).

Example 2

Li_(1+x)Ni_((2−4x)/3)M_((1+x)/3)O₂, [0.15<x≦0.3], M=Sb or Nb

To prepare Li_(1+x)Ni_((2−4x)/3)M_((1+x)/3)O₂ [M=Sb or Nb], Li₂CO₃,NiCO₃, and Sb₂O₅ (or Nb₂O₅) were used as precursors. More than 5% excessLi₂CO₃ from the stoichiometric amount needed to synthesizeLi_(1+x)Ni_((2−4x)/3)M_((1+x)/3)O₂, [0<x≦0.3] was used to compensate forpossible Li loss during high temperature solid state reaction. Theprecursors were dispersed into acetone and ball-milled for 24 hours anddried overnight to prepare the precursor mixture. The mixture was firedat 800° C. for 15 hours under O₂ gas, and manually ground to obtain thefinal products.

Carbon coating can be applied 1) to improve the cycling performance ofLi_(1+x)Ni_((2−4x)/3)M_((1+x)/3)O₂ [M=Sb or Nb] by decreasing theparticle size upon the carbon coating process, and 2) to improveelectronic conductivity of the compounds. Sucrose (C₁₂H₂₂O₁₁) can beused as a carbon precursor, and was mixed in a planetary ball-mill withLi_(1+x)Ni_((2−4x)/3)M_((1+x)/3)O₂ [M=Sb or Nb] in weight ratio between90:10 and 70:30 of active material to sucrose. Then the mixture can beannealed between 400° C. to 800° C. for 2 to 6 hours under O₂ gas.

For electrochemical tests, Swagelok cells were assembled under Aratmosphere in a glove box. For the cathode fabrication, ˜80 wt % of theactive compounds, ˜15 wt % of carbon black, and ˜5 wt % of PTFE binderwere intimately mixed by hands or planetary ball-mill.

Example 3

Li_(1+x)Ni_((3−5x)/4)Mo_((1+x)/4)O₂, [0.15<x≦0.3]

To prepare Li_(1+x)Ni_((3−5x)/4)Mo_((1+x)/4)O₂, Li₂CO₃, NiCO₃, and MoO₂can be used as precursors. More than 5% excess Li₂CO₃ from thestoichiometric amount needed to synthesizeLi_(1+x)Ni_((3−5x)/4)Mo_((1+x)/4)O₂ [0<x≦0.3] can be used to compensatefor possible Li loss during high temperature solid state reaction. Theprecursors can be dispersed into acetone and ball-milled for 24 hoursand dried overnight to prepare the precursor mixture. The mixture can befired at 800° C. for 10 hours under O₂ gas, and manually ground toobtain the final products.

Carbon coating can be applied 1) to improve the cycling performance ofLi_(1+x)Ni_((3−5x)/4)Mo_((1+x)/4)O₂ by decreasing the particle size uponthe carbon coating process, and 2) to improve electronic conductivity ofthe compounds. Sucrose (C₁₂H₂₂O₁₁) can be used as a carbon precursor,and it can be mixed in a planetary ball-mill withLi_(1+x)Ni_((3−5x)/4)Mo_((1+x)/4)O₂ in weight ratio between 90:10 and70:30 of active material to sucrose. Then the mixture can be annealedbetween 400° C. to 800° C. for 2 to 6 hours under O₂ gas.

For electrochemical tests, Swagelok cells can be assembled under Aratmosphere in a glove box. For the cathode fabrication, ˜80 wt % of theactive compounds, ˜15 wt % of carbon black, and ˜5 wt % of PTFE bindercan be intimately mixed by hands or planetary ball-mill.

Li_(1+x)Ni_((3-5x)/4)Mo_((1+x)/4)O₂ may exhibit the maximum capacity asshown in the dotted curve in FIG. 3, and the minimum capacity(determined by accessible lithium atoms per formula unit) as shown inthe dotted curve in FIG. 5 if sufficient voltage can be applied withinthe voltage windows of electrolytes.

Example 4

Li_(1+x)Ru_(2x)M_(1−3x)O₂, [0.15<x<0.333], M=Co, Ni, Fe

To prepare Li_(1+x)Ru_(2x)M_(1−3x)O₂, Li₂CO₃, RuO₂, and CoCO₃, NiCO₃,FeCO₃ for M=Co, Ni, Fe, respectively, can be used as precursors. Morethan 5% excess Li₂CO₃ from the stoichiometric amount needed tosynthesize Li_(1+x)Ru_(2x)M_(1−3x)O₂ [0<x<0.333] can be used tocompensate for possible Li loss during high temperature solid statereaction. The precursors can be dispersed into acetone and ball-milledfor 24 hours and dried overnight to prepare the precursor mixture. Themixture can be fired at 600° C. for 10 hours under O₂ gas, and manuallyground to obtain the final products.

Carbon coating can be applied 1) to improve the cycling performance ofLi_(1+x)Ru_(2x)M_(1−3x)O₂ by decreasing the particle size upon thecarbon coating process, and 2) to improve electronic conductivity of thecompounds. Sucrose (C₁₂H₂₂O₁₁) can be used as a carbon precursor, and itcan be mixed in a planetary ball-mill with Li_(1+x)Ru_(2x)M_(1−3x)O₂ inweight ratio between 90:10 and 70:30 of active material to sucrose. Thenthe mixture can be annealed between 400° C. to 800° C. for 2 to 6 hoursunder O₂ gas.

For electrochemical tests, Swagelok cells can be assembled under Aratmosphere in a glove box. For the cathode fabrication, ˜80 wt % of theactive compounds, ˜15 wt % of carbon black, and ˜5 wt % of PTFE bindercan be intimately mixed by hands or planetary ball-mill.

Li_(1+x)Ru_(2x)M_(1−3x)O₂ [0<x<0.333] may exhibit the maximum capacityas shown in the dash-dotted curve in FIG. 3, and the minimum capacity(determined by accessible lithium atoms per formula unit) as shown inthe dash-dotted curve in FIG. 5 if sufficient voltage can be appliedwithin the voltage windows of electrolytes.

Example 5

Li_(1+x)Fe_(1-y)Nb_(y)O₂ (0.15<x≦0.3, 0<y≦0.3)

To prepare Li_(1+x)Fe_(1-y)Nb_(y)O₂ (0<x≦0.3, 0<y≦0.3), Li₂CO₃, FeCO₃,and Nb₂O₅ can be used as precursors. More than 5% excess Li₂CO₃ from thestoichiometric amount needed to synthesizeLi_(1.125)Fe_(0.7)Nb_(0.175)O₂ can be used to compensate for possible Liloss during high temperature solid state reaction. The precursors can bedispersed into acetone and ball-milled for 24 hours and dried overnightto prepare the precursor mixture. The mixture can be fired at 600° C.for 10 hours under O₂ gas, and manually ground to obtain the finalproducts.

Carbon coating can be applied 1) to improve the cycling performance ofLi_(1+x)Fe_(1-y)Nb_(y)O₂ by decreasing the particle size upon the carboncoating process, and 2) to improve electronic conductivity of thecompounds. Sucrose (C₁₁H₂₂O₁₁) can be used as a carbon precursor, and itcan be mixed in a planetary ball-mill with Li_(1+x)Fe_(1-y)Nb_(y)O₂ inweight ratio between 90:10 and 70:30 of active material to sucrose. Thenthe mixture can be annealed between 400° C. to 800° C. for 2 to 6 hoursunder O₂ gas.

For electrochemical tests, Swagelok cells can be assembled under Aratmosphere in a glove box. For the cathode fabrication, ˜80 wt % of theactive compounds, ˜15 wt % of carbon black, and ˜5 wt % of PTFE bindercan be intimately mixed by hands or planetary ball-mill.

Li_(1+x)Fe_(1-y)Nb_(y)O₂ (0.15<x≦0.3, 0<y≦0.3) may exhibit the maximumcapacity as shown in the dotted curve in FIG. 3 and the minimum capacity(determined by accessible lithium atoms per formula unit) as shown inthe dotted curve in FIG. 5 if sufficient voltage can be applied withinthe voltage windows of electrolytes.

What is claimed is:
 1. A lithium metal oxide characterized by a generalformula Li_(x)M_(y)O₂ wherein 0.6≦y≦0.85, 0≦x+y≦2, and M being one ormore of a metallic species chosen from the group consisting of Al, Ti,V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Nb, Mo, Ru, Sn and Sb; wherein saidoxide, as synthesized, has a random or partially random distribution ofLi cations and M cations in the oxygen arrangement of the rock-saltstructure, as measurable by XRD, wherein the lithium metal oxide hassubstoichiometric amount of lithium.
 2. An electrode comprising alithium metal oxide characterized by a general formula Li_(x)M_(y)O₂wherein 0.6≦y≦0.85, 0≦x+y≦2, and M being one or more of a metallicspecies chosen from the group consisting of Al, Ti, V, Cr, Mn, Fe, Co,Ni, Cu, Zn, Zr, Nb, Mo, Ru, Sn and Sb; wherein said oxide, assynthesized, has a random or partially random distribution of Li cationsand M cations in the oxygen arrangement of the rock-salt structure, asmeasurable by XRD.
 3. A lithium battery comprising the electrodematerial of claim
 2. 4. A device comprising the lithium battery of claim3.
 5. The device of claim 4, wherein the device is a portable electronicdevice, an automobile, or an energy storage system.
 6. A lithium-ioncell comprising the electrode material of claim 2.